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INTRODUCTORY
Pre-scientific metaphysics of common sense

Gives us a general, vague knowledge of the general principles of being and knowledge, valuable even to the extent of knowing the existence of God and some basic truths about him.

Summa theologiae II, q. 10, a. 7:

Many of the gentiles received revelation of Christ... If, however, some were saved without receiving any revelation, they were not saved without faith in a mediator, for, though they did not believe in Him explicitly, they did, nevertheless, have implicit faith through believing in Divine providence, since they believed that God would deliver mankind in whatever way was pleasing to Him, and according to the revelation of the Spirit of those who knew the truth, as stated in Job 35:11: "Who teaches us more than the beasts of the earth."

Knowledge of existence of God:

This knowledge does not extend to the particular science of things of this world, which we are totally ignorant of until we learn them by ourselves or from a teacher.

QD de veritate 11, a. 1

We must give a similar explanation of the acquisition of knowledge. For certain seeds of knowledge pre-exist in us, namely, the first concepts of understanding, which by the light of the agent intellect are immediately known through the species abstracted from sensible things. These are either complex, as axioms, or simple, as the notions of being, of the one, and so on, which the understanding grasps immediately. In these general principles, however, all the consequences are included as in certain seminal principles. When, therefore, the mind is led from these general notions to actual knowledge of the particular things, which it knew previously in general and, as it were, potentially, then one is said to acquire knowledge.

This knowledge is intuitive, confused and non-analytic. In traditional cultures it may be expressed in the form of stories or proverbs.

Scientific metaphysics begins with wonder, which is a desire to understand something we do not yet understand, as we see in the Prologue.

The value of knowledge and order of learning

Exposition of Liber de causis, preface

The highest felicity of man consists in the best activity belonging to his highest power, that is, his intellect, in attaining the most intellectual object. Furthermore, since an effect is known through its cause, it is clear that a cause is in its nature more intelligible than its effects, although at times effects are better known to us than causes, because our knowledge of universal and intelligible causes has been gathered from the particular things which fall under the senses. Absolutely speaking, therefore, the first causes of things must be in themselves the highest and the most intellectual objects, since they are the highest beings and the highest truths, being for other things the cause of their essence and truth, as the philosopher makes clear in the Metaphysics. It remains, however, that such primary causes are less well known as far as we are concerned, for our intellect stands to them as the eye of an owl to the light of the sun, which, owing to its excessive clarity, cannot be perfectly perceived.

It is proper, therefore, that the highest felicity that man can obtain in this life should consist in the contemplation of the first causes; for the little that can be known about them is more lovable and noble than everything that can be known about lesser things, as is clear from the words of the Philosopher in his On the Parts of Animals. And it is through the completion of this knowledge in us after the present life that man is made perfectly happy, according to the words of the Gospel: "This is eternal life, that they may know you, the only true God."

So the principal aim of the philosophers was that, through all their investigations of things, they might come to know the first causes. That is why they placed the science concerned with first causes last, and allotted the final period of their lives to its consideration. They began first of all with logic, which teaches the method of the sciences. Second, they went on to mathematics, which even boys are capable of learning. Third, they advanced to the philosophy of nature, which requires time because of the needed experience. Fourth, they proceeded to moral philosophy, of which a young person cannot be a suitable student. And finally they applied themselves to divine science, whose object is the first causes of things.

Commentary on the Nichomachean Ethics, Book 6, lect. 7:

[Aristotle] raises the question why a boy can become a mathematician but cannot become wise, that is to say a metaphysician or physicist, in other words a natural philosopher. His reply to this, as far as the philosophy of nature is concerned, is that mathematical entities are known by abstraction from sensible things, which are the objects of experience, and as a result a great length of time is not needed to grasp them. The principles of natural things, however, which are not separated from sensible things, are known through experience, for which much time is needed.

As far as wisdom is concerned, he adds that the young do not believe, that is, do not understand with their mind, things pertaining to wisdom or metaphysics, though they may speak them with their lips. But the nature of mathematical entities is not obscure to them, because their definitions concern things that can be imagined, whereas the objects of metaphysics are purely intelligible. Now the young can easily grasp what falls under the imagination, but they cannot understand with their mind whatever goes beyond sense and imagination, for their minds are not yet vigorous and trained to such reflections because of the shortness of their lives and the many physical changes they are undergoing.

So the proper order of learning will be the following. First, boys should be instructed in logical matters, because logic teaches the method of the whole of philosophy. Second, they are to be instructed in mathematics, which does not require experience and does not transcend the imagination. Third, they should be trained in the natural sciences which, though not transcending sense and imagination, nevertheless require experience. Fourth, they are to be instructed in the moral sciences, which require experience and a soul free from passion, as is said in the first book. Fifth, they should be taught matters concerning wisdom and divine science, which go beyond the imagination and require a vigorous mind.

Certainty

De veritate 10, a. 8, ad 8

Knowledge of the soul is most certain for this reason that each one experiences within himself that he has a soul and that the acts of the soul are within him.

De veritate 14, a. 1, ad 7

Certitude can mean two things. The first is firmness of adherence, and with reference to this, faith is more certain than any understanding of principles and scientific knowledge. For the first truth, which causes the assent of faith, is a more powerful cause than the light of reason, which causes the assent in the intellectual habitus of first principles or in science. The second kind of certitude is the evidence of that to which assent is given. Here faith does not have certainty but science and the habitus of first principles do.

S.T. I, 1, 5, ad 1

It may well happen that what is in itself the more certain may seem to us less certain because of the weakness of our intellect, which is dazzled by the clearest objects of nature, as the owl is dazzled by the light of the sun.

Commentary on Posterior Analytics, I, lesson 7

Not all science is demonstrative, that is, acquired by demonstration. It should be understood here that Aristotle takes science broadly for any certain knowledge, and not as opposed to understanding, as when it is said that science deals with conclusions, but understanding with principles. That certain knowledge of some things is had without demonstration, he proves thus: It is necessary to know the prior things from which demonstration proceeds. At some point these must be reduced to things that are immediately certain. Otherwise it would be necessary to say that between two extremes, that is, the subject and predicate, there would be an infinite number of middle terms in act; even further, that there could be no two things between which there would not be an infinity of middles. In whatever way middles are taken, there must be something immediate to what follows. But since those which are immediate are prior, they must be indemonstrable. Therefore it is evident that knowledge of some things must be had without demonstration.

Universality

Commentary on Posterior Analytics, I, lesson 17, n. 5

Since the principles of a lower science are/proved by the principles of a superior science, one does not proceed from the caused to the causes, but conversely. Whence such a process must be for these things that are prior and better known absolutely. Therefore, that must be better known which belongs to the superior science from which the principles of the inferior are proved, and the better known is that by which all else is proved while it itself is not proved by anything prior to it. Consequently, the superior science will be more truly science than the lower; and the supreme science, namely first philosophy, will be most truly science.

Liberal character

Aristotle: On the parts of animals I, 5, 644b33

The scanty conceptions to which we can attain of celestial things give us, from their excellence, more pleasure than all our knowledge of the world in which we live; just as a half glimpse of persons that we love is more delightful than a leisurely view of other things, whatever their number and dimensions.

Difficulties

Commentary on the Ethics VI, lesson 7, 1210-1211

As far as wisdom is concerned, he [Aristotle] adds that young persons do not believe—that is, do not understand with their mind—the objects of wisdom or metaphysics, although they may speak them with their lips. But regarding mathematical entities, their essences are not hidden from them, because the definitions in mathematics concern things that are imaginable, whereas objects of metaphysics are purely intellectual. Now young people can easily grasp what falls under the imagination. But they cannot understand with their minds what transcends sense and imagination, because their intellects are not trained to such consideration owing to the shortness of their life and the many changes of their nature.

Consequently, the fitting order of learning will be the following: first, boys should be instructed in logic, because logic teaches the method of the whole of philosophy. Second, they should be instructed in mathematics, which does not require experience and does not transcend the imagination. Third, they should learn the natural sciences, which although not transcending sense and imagination, nevertheless require experience. Fourth, they should be instructed in the moral sciences, which require experience and a soul free from passions, as is said in the first book. Fifth, they should learn metaphysics and divine science, which transcend the imagination and demand a robust intellect.